Cable clamping apparatus for junction box

ABSTRACT

In junction boxes for coupling T.V. signals and low frequency power waves on a coax line to a plurality of users, the T.V. signals are coupled via connections in a first compartment to a plurality of coax cables, and the low frequency power wave are coupled via low pass-filters to IDC connections in a second compartment. 
     Leads from users are passed through a chamber on the wall of the second compartment containing a self-healing, self-supporting insulating substance and attached to the IDC connectors. The IDC connectors permit the lead to be paired through them so that an installer can know when the leads are properly partitioned.

This is a Division of application Ser. No. 08/814,491, filed Mar. 10,1997, pending.

BACKGROUND OF THE INVENTION

In Cable TV and other RF signal distribution systems, it is usuallyrequired to tap off RF energy from a main distribution coaxial cable forsubscriber service through a drop feed cable. A known tap off device toaccomplishing this is a multi-tap.

A variety of tap values are available in order to deliver the correctsignal level to the service drop regardless of signal level in thetransmission cable at that particular point in the system.

A multi-tap consists of a removable tap plate and a housing. The tapplate and housing must be installed in the manner to be completelyhermetically sealed so that moisture does not penetrate into the device.

When, however, additional services such as those that provide telephoneservice to a user, the power source to energize the necessary equipmentwill be provided by the cable system through the same coaxial cablecarrying both AC power and the RF signal. Within the tap, an RF signalis tapped off to appropriate RF connectors, which are an integral partof the tap plate. AC power is provided through the IDC (InsulationDisplacement Connector) connector terminal inside the tap.

Typically a coaxial cable with an F-Type connector is connected to thetap RF ports to tap off an RF signal to a subscriber TV set, and a pairof wires are connected to the AC connector terminal of the tap to tapoff AC power to subscriber equipment.

Thus it is necessary that ends of the leads for carrying power to theuser be inserted into the hermetically sealed junction box, but it hasbeen difficult to do this in such manner as to preserve the hermeticalseal. For example, such a junction box can be a multi-tap for cable TV.One method has been to simply pass the leads between the cover and thebody of the box in the hope that the gasket between them will providethe seal. Unfortunately, however, the gasket material does not flowcompletely around the leads and therefore cannot provide a hermeticseal. The problem gets worse each time the box is opened. Typically, theleads carry AC power from the multi-tap for example, to a subscriber oruser.

Furthermore, connection between a terminal in the junction box and alead from the special cable that has been inserted into the junction boxhas heretofore been effected by an IDC connector within the box having aterminal for connection to circuits, a blind input port into which thelead is inserted, and mechanically operable means for cutting throughthe insulation of the lead so as to connect it to the terminal.

One of the problems encountered is that it has been difficult for acable installer to know whether or not the connection has been madebecause of the possibility that the lead is not properly located withinthe IDC connector. It might, for example, be deflected so as not toreach the position where its insulation will be cut so as to make thedesired connection to the terminal. This problem is emphasized bydeleterious conditions under which the connection is sometimes made.

SUMMARY OF THE INVENTION

A junction box constructed in accordance with this invention provides away of introducing leads into it without in any way affecting theexcellent seal maintained between its cover and its body regardless ofthe number of times the cover and power are removed and installed. Thisis effected by forming a chamber adjacent the outside of the junctionbox through which insulated leads for power etc., are inserted. Sealingis achieved by a sealant within the chamber that is self-healing,self-supporting and insulating. A sealant suitable for this purpose isavailable from the Ray Chem Corp. of 300 Constitution Drive, Menlo Park,Calif. 94025, or is available from the AMP Manufacturing Co. as Part No.990705-1 having a material specification 100-1191 and a processspecification 119-2190, for example,

Whether insulating material is suitable as a sealant can be determinedby placing some in the bottom of a paper cup, filling the cup with waterand ramming a sharp instrument such as an ice pick or a wire through thesealant and the bottom of the cup and withdrawing the instrument. If thematerial is self-healing as required, water will not leak through thebottom of the cup because the hole in the sealant made by the instrumentis almost immediately filled. The material must be self-supporting ascan be demonstrated by its remaining in the cup when the cup is turnedupside down.

With such sealant, a lead can be inserted through the chamber and therewill be no aperture through which moisture can pass because the sealantwill form an intimate contact with it at all points. Furthermore, thelead can be withdrawn and reinserted many times without causing a leak.

Another distinct advantage is the fact that the IDC (InsulationDisplacement Connector) within the junction box has inlet and outletports through which a lead can be inserted so that even if thevisibility is very poor, a cable installer can tell by feeling theoutput port of the contact whether a lead is properly installed.

BRIEF SUMMARY OF THE DRAWINGS

FIG. 1 illustrates a prior art IDC connector;

FIG. 2 is an exploded isometric assembly view of a multi-tap assemblylooking down on the bottom when installed;

FIG. 3 is a bottom view of the junction box of FIG. 2 of the inventionwhen assembled with its cover closed;

FIG. 4 is a bottom view of the junction box of FIG. 2 of the inventionwith its cover open;

FIG. 5 is a cross-sectional isometric view of a co-joined coaxial cableand four pairs of power cables;

FIG. 6 is a view of a portion of the junction box of the invention ofFIG. 2 showing how the leads are inserted through the chamber and intothe junction box;

FIG. 7A is an isometric view of an IDC connector in which the inlet andoutlet ports are such as to direct the uncut lead upward from a junctionbox of the invention;

FIG. 7B is an isometric view of an IDC connector in which the inlet andoutlet ports of an IDC connector are such as to direct the uncut leadparallel to the bottom of the associated junction box of the invention;

FIG. 8A is a partial cross-sectional view taken along 8A--8A of FIG. 6showing a chamber containing sealant and an open IDC connector in whichthe inlet and outlet ports are such that an uncut lead slants upwardlythrough the chamber;

FIG. 8B is a partial cross-sectional view like taken along 8B--8B ofFIG. 6 showing the position of a closed IDC connector making electricalconnection through an insulated wire;

FIG. 8C is a partial cross-sectional view of a chamber containingsealant and an open IDC connector in which the leads passperpendicularly through the chamber for another embodiment of theinvention;

FIG. 8D is a partial cross-sectional view like that of FIG. 86C showingthe position of a closed IDC connector making electrical connectionthrough an insulated wire;

FIG. 8E is a partial cross-sectional view of a chamber containingsealant and an open IDC connector showing inlet and outlet openings inthe channel shaped like funnels to aid in guiding an insulated wirethrough them;

FIG. 9A is an outside and partial cross-sectional view showing a chamberof a multi-tap housing containing the sealant and further showing inletopenings of the chamber for the leads at positions corresponding totheir positions in FIGS. 8A and 8B in accordance with an embodiment ofthe invention;

FIG. 9B is an outside and partial cross-sectional view showing a chamberof a multi-tap housing containing sealant and further showing inletopenings of the chamber for the leads at positions corresponding toFIGS. 8C and 8D;

FIG. 10 is an isometric view of a gasket for closing off the outside ofopen slots of a multi-tap housing through which electrical cable passesto a chamber containing sealant when not in use;

FIG. 11 is an outside view of a multi-tap housing illustrating use ofthe gasket of FIG. 10 for one embodiment of the invention;

FIG. 12 is an exploded isometric view of a preferred embodiment of amulti-tap junction box of the invention.

FIG. 13 is a bottom view of a junction box of FIG. 12 of the inventionwhen assembled with its cover open;

FIG. 14 is a view of a portion of the junction of FIG. 12 with the coverremoved showing how cables and associated leads are connected to thejunction box;

FIG. 15A is a partial cross-sectional view taken along 15A--15A of FIG.14;

FIG. 15B is a partial cross-sectional taken along 15B--15B of FIG. 14;

FIG. 16 is an outside and partial cross-section view of the multi-taphousing of FIG. 14;

FIG. 17 is a pictorial view of a seal plug for the preferred embodimentof the invention of the multi-tap housing of FIG. 12;

FIG. 18 is an elevational view of a side of the multi-tap housing ofFIG. 12 showing some of the plugs of FIG. 17 installed therein;

FIG. 19 is an elevational and partial cross-sectional view of theembodiment of the invention of FIG. 12 incorporating an illustrativeembodiment for the cable clamping mechanism;

FIG. 20 is a cross-section 20, 20 of FIG. 14;

FIG. 21 is an external view of a low pass filter of this invention;

FIG. 22 is an exploded partly cut away view of a low pass filter of thisinvention; and

FIG. 23 is schematic diagram of one circuit for low pass filter of thisinvention.

DETAILED DESCRIPTION OF THE INVENTION

In the prior art IDC shown in FIG. 1, terminals 2 and 4 are respectivelyconnected to U shaped spades 6 and 8 within an enclosure 10 in whichinsulated leads to be connected to the terminals 2 and 4 are passed viaports 12 and 14 in a member 16. The member 16 pivots about an axis 18 sothat when it is pressed down, leads in the ports 12 and 14 arerespectively forced into the spades 6 and 8 that cut through theinsulation so as to make contact between the conductors in the leads andthe spades 6 and 8. Although not shown, the passageways associated withthe ports 12 and 14 are blind, and the spades 6 and 8 are immersed insealant 20 so that the connections with the leads are protected from airand moisture. The sealant used is the same as is used in this invention.

In discussing the various figures of the drawings, like parts will bedesignated in the same way.

Reference is made to FIGS. 2 and 3, which are bottom views of thejunction box when installed. FIG. 2, an input coaxial cable 22 thatcarries the TV signals and may carry low frequency AC power is coupledby a coaxial port 24 to the interior of a first closed compartment 26.Circuits within the compartment 26 couple the TV signals on the cable 22to coaxial connectors 28, 30, 32, 34, 36, 38, 40, and 42 that extendoutwardly from the top plate 43 of the compartment 26 and to an outputcoaxial cable 44 that is coupled to the circuits within the compartment26 by a coaxial port 46. When not in use, the connectors 28-42 areprotected by 75 ohm load terminators such as indicated at 28', 30', 36',38', and 40' in FIG. 3. Thus TV signals arrive on the input coaxialcable 22 and leave on the output coaxial cable 44. As described in theU.S. Patent application entitled "Cable TV Multi-Tap UninterruptedSignal/Power Throughport", bearing Ser. No. 08/489,726, filed on Jun.13, 1995 and assigned to the same assignee as this invention, these TVsignals continue to flow between the input cable 22 and the output cable44 even though work is being done on the circuits within the compartment26 that otherwise would require their interruption. The top 43 of thecompartment 26 is fastened to its bottom by threaded bolts 50, 50A, 52,and 54. The bolt 52 is not shown in FIG. 2, but would be behind theconnector 30.

A second compartment or box 56 is integral with an integrated part ofthe compartment 26, and threaded bolts 58, 60, 62, 66, 68, and 70 serveto fasten a cover 64 to the compartment 56. When the bolts are notfastened, the cover 64 can be pivoted about hinges 72 and 74. A ledge 73to which power cables are to be clamped extends outwardly from thebottom of the compartment 56 and is parallel thereto. When the cover 64is closed, a projection 75 thereof overlies the ledge 73.

FIG. 4 shows the bottom of the compartment 56 of FIG. 2 with the cover64 open so as to reveal a circuit board 76 that is coupled in a mannerdescribed below to the coaxial cable 22 through a filter assembly 302shown in FIG. 20 so as to provide low frequency AC power to terminals,not shown, for IDC connectors 78, 80, 82, 84, 86, 88, 90, and 92.Twisted pairs of insulated leads from a power cable like 128 of FIG. 5that leads to a user are to be inserted in each of the IDC connectors78-92 in a manner to be particularly described by reference to FIG. 6.The leads are respectively held by clamps 94, 96, 98, 100, 102, 104,106, and 108 in the semi-cylindrical grooves indicated by the samenumbers primed as will also be explained by reference to FIG. 6.

With the cover 64 open, the top 110 of a side wall 111 of thecompartment 56 as well as a gasket 112 within channel 112' extendcompletely around the top 110 are visible. When the cover 64 is closed,the gasket 112 will be sandwiched there between. This is necessary inorder to provide a tight moisture seal. The bolts 58, 60, 62, 66, 68,and 70 pass through holes in the top 64 and are threaded in holes in thetop 110, indicated by the same numbers primed so as to hold the cover 64in its sealed position when tightened.

As can be seen, insulated leads carrying the AC power must pass from theIDC connectors 78-92, FIG. 4, that are inside the second compartment 56to a point outside it i.e., they must pass beyond the side wall 111 to auser via a power cable 128 such as shown in FIG. 5. In order to do this,the previous practice has been to pass them between the gasket 112 andthe cover 64, but this has not provided a satisfactory seal.

In accordance with this invention, chambers 114 and 116, as seen inFIGS. 2, 4, and 6, are provided adjacent respective portions of theoutside of the side wall 111 of the compartment 56 and contain thesealant previously referred to. As shown in FIG. 6, cables 118, 120,122, and 124 having cross-sections such as shown in FIG. 5 are broughtfrom a junction box to the users' location. Each of these cables iscomprised of a coax cable 126 that is joined to the power cable 128along their length. Although only one pair of insulated power leads isrequired for each user, it is customary to provide four leads 130, 132,134, and 136 so as to provide an extra pair that can be used in theevent a first pair fails. At the junction box, the ends of the coaxialcables such as 126 and the power cables such as 128 are separated andthe coaxial cables are coupled to respective coaxial connectors 28-42shown in FIGS. 2, 3, and 4.

FIG. 6 illustrates the various positions that insulated leads of a powercable such as 128 will have as they are being installed. Insulated leads138 and 140 from a power cable 142 have just been cut so as to be readyfor insertion. Insulated leads 144 and 146 from a power cable 148 havebeen passed through the chamber 114 and inserted into respective inletports, not shown, in the IDC connector 82. Activating levers 152 and 150of the IDC connectors 84 and 82 are in the non contact or raisedposition. Insulated leads 154 and 156 from a power cable 158 have beeninserted through the inlet and outlet ports, not shown, of the IDCconnector 80, and its lever 159 has been pressed to make electricalcontacts between the leads 154 and 156 and their respective terminals.Insulated leads 160 and 162 from a power cable 164 have been cut off bythe cable installer and the clamp 94 tightened to hold the power cable164. The lever 166 of the IDC connector 78 remains closed.

The fact that insulated leads can extend completely through their IDCconnector such as the IDC connector 80 in the case of the leads 154 and156 makes it possible for a cable installer to tell by feel and/or sightwhen they are in the desired position.

FIG. 7A is an external isometric view of the angles at which power leadsare introduced into and leave an IDC when a chamber 170 shown in FIGS.8A and 8B is used, and FIG. 7B is an external isometric view of theangles at which power leads are introduced into and leave an IDC when achamber 170' of FIGS. 8C and 8D is used. Any of the chambers 170, 170',and 170" can be used for the chambers 114 and 1 16 in FIGS. 2, 4, and 6,and an IDC connector 174 shown in FIGS. 8A, 8B, 8C, 8D, and 8E can beused for any of the IDC connectors 78, 80, 82, 84, 86, 88, 90, and 92 ofFIGS. 2, 4, 6, 12, and 14. The chambers 170, 170', and 170" are filledwith the sealant 172.

The IDC connector 174 of FIGS. 8A, 8B, 8C, 8D, and 8E can be used forthe IDC connectors 78 through 92. The IDC connector 174 of FIGS. 8A, 8C,and 8E is in an open position as would be seen in section 8A, 8A of FIG.6, and the IDC connector 174 of FIGS. 8B and 8D is in a closed positionas would be seen in section 8B, 8B of FIG. 6. In FIGS. 8A, 8B, 8C, 8D,and 8E, the IDC 174 is comprised of a base 176, a side wall 178 seenonly in FIGS. 7A and 7B, an opposing parallel side wall 178', and alever 180 pivoted at 182 to move in an opening 179 between the sidewalls 178 and 178'. A screwdriver slot 181 in the top of the lever 180permits the lever 180 to be raised to an open position. A passageway 184within the lever 180 passes from an inlet port 186 adjacent the pivotpoint 182 to an outlet port 188. An outlet port 190 in the side wall 111communicates with the inlet port 186 when the lever 180 is in the raisedposition shown in FIGS. 8A and 8C. A slot 192 within the lever 180 istransverse to the passageway 184. A spade 194 of conductive materiallike the spades 6 and 8 of FIG. 1 that have one end U shaped as seenfrom the side is mounted in the base 176 so as to be in registrationwith the slot 192. When the lever 180 is lowered, as shown in FIGS. 8Band 8D, the spade 194 cuts through the insulation of a lead within thepassageway 184 and makes electrical contact with its conductor. In FIGS.8A and 8C, the lead 146 is seen, and in FIGS. 8B and 8D the lead 156 isseen.

The base 176 of the IDC 174 is mounted on the circuit board 76, and theother end 200 of the spade 194 serves as a terminal that can beconnected to an AC power source in the circuit. A spade 201 shown indotted lines because it is behind the plane of the cross-section cutsthe insulation of the other insulated lead of a pair, not shown, to makecontact with a terminal 201'.

FIG. 8A is a section 8A, 8A of FIG. 6 showing the insulated lead 146just before it has been inserted far enough to pass beyond the outletport 188 of the passageway 184 in the lever 180 of the IDC 82 when achamber construction 170 is used. In a chamber construction 170, apassageway 202 passes completely through the wall 111 of compartment 26and the outer wall 206 of the chamber 114 so as to connect the opening190 to an opening 204. The angle of the passageway 202 is aligned withthe passageway 184 of the lever 180 when the lever 180 is up so as tomake it easier to insert the lead 146. The same is true for the lead144, which is not seen in this section.

FIG. 8B is a section 8B, 8B of FIG. 6, showing the insulated lead 156that has been thrust entirely through the passageway 184 of the IDC 80.The lever 180 has been lowered so as to make the desired electricalconnection between the conductor, not shown, of the lead 156 and thespade 194, but the lead 156 has not been cut. The same is true for thelead 154, which is not seen in this section. The clamp 96 is thentightened to hold the cable 158 in place, and the lead 156 is cut justoutside the outlet port 188 so as to be like the lead 162 in the IDC 78.

FIGS. 8C and 8D correspond respectively to the FIGS. 8A and 8B exceptthat a chamber construction 170' is used in which the inlet port 204' isat the same height in the wall 111 as the outlet port 190 so that thepassageway 202' makes an angle with the passageway 184 when the lever180 is raised but is coaxial therewith when the lever 180 is lowered tomake electrical contacts.

FIG. 8E is like FIG. 8A except that an opening 210 in the wall 110 ofthe chamber 170", and an opening 212 in the outer wall 206 of thechamber 170" are connected by a funnel shaped passageway 202' so as tobetter guide the lead 196.

It is preferable to cover the top of the sealant 172 in the chambers170, 170' and 170" with a layer 208 of rubber or the like that adheresto the sealant 172.

FIG. 9A is a front view of the compartment 56 of FIGS. 2, 3, 4, and 6with the cover 64 removed when the sealing chamber 170 of FIGS. 8A and8B is used and wherein respective pairs of inlet openings like 204 areimmediately above the clamps 94, 96, 98, and 100. The positions of pairsof outlet openings like 190 are shown in the right half dashed linesbecause they are in the inner surface of the wall 111. The right half ofFIG. 9A is in a partial cross-section showing the sealant 172 and theoverlying rubber mat 208. Note that there are semi-circular grooves,94', 96', 98', and 100' under the respective clamps 94, 96, 98, and 100and semi-circular grooves 102', 104', 106', and 108' under therespective clamps 102, 104, 106, and 108 so as to provide a snug fitaround a power cable when present.

FIG. 9B is the same as FIG. 9A except that the pairs of openings shownin its left half have locations like the opening 204' of FIGS. 8C and 8Dthat are spaced farther from the clamps 94, 96, 98, and 100.

In FIG. 11, a gasket 214 like that shown in FIG. 10 is permanentlyadhered in an opening 218 in a wall 222 that depends downwardly from thefront of the cover 64 as also shown in FIG. 2 so that halves ofcylindrical plugs 224, 226, 228, and 230 of FIG. 10 that are removablyadhered to semi-circular grooves indicated by lines 224', 226', 228',and 230' fit into the grooves 94'-100'. When a power cable such as 128of FIG. 5 is to be installed, a plug such as 224' of FIG. 10 is removed,and a power cable having the same diameter as the plug takes its placeso that there are no leaks through the depending wall 222 to permit theentrance of moisture. In FIG. 11, a gasket 214 like that of FIG. 10 isdisplaced from the opening 220 in the wall 222 so as to reveal thegrooves 102'-108' and the clamps 102-108 located behind them. The gasket214 prevents dirt and insects from getting into the compartment 56.

FIG. 12 is an exploded isometric assembly drawing of a preferred form ofa junction box of this invention that is like that of FIG. 2 except forthe way in which the power cables like 128 of FIG. 5 are clamped intoplace and the manner in which the openings between the front wall 222and the ledge 73 for receiving power cables when the cables are notpresent are sealed. Also, the mounting ledge 73 is elevated closer tothe wire holes 204' to insure the power cables 158 are not bent but areretained in a straight configuration as shown in FIG. 15B, for example.Only the differences between FIG. 12 and FIG. 2 are now described.

In this preferred embodiment of the invention, lugs 232 and 234 areprovided at opposite ends of the ledge 73, and a lug 236 is provided atits center. A plate 238 is fastened to the lugs 232 and 236 by screws239 and 240, and a plate 242 is fastened to the lug 236 and the lug 234by screws 243 and 244. Thus, the plate 238 passes over and is spacedfrom the grooves 94', 96', 98', and 100', and the plate 242 passes overand is spaced from the grooves 102', 104', 106', and 108' whenassembled. Clamp bolts 246, 248, 250, and 252 are threaded through theplate 238 in respective registration with the grooves 94', 96', 98', and100', and clamp bolts 254, 256, 258, and 260 are threaded through theplate 242 in respective registration with the grooves 102', 104', 106',and 108'. As illustrated by the bolt 246, each of the bolts 246 through260 are indented at one end so as to receive an Allen® wrench orPhilips® head or slot screw driver and have a head 262 at the other.Thus, when a power cable like 128 of FIG. 5 is inserted in any one ofthe grooves 94'-108', the corresponding bolt can be tightened so as toretain it in position.

Provision of a dirt and insect seal when a power cable is in a groovelike 94' is accomplished in the following manner. The plate 238 comes incontact with the tops of fins 263, 264, and 266 that are respectivelylocated between the groove pairs 94', 96'; 96', 98', and 98', 100', andthe plate 242 comes in contact with the tops of fins 270, 272, and 274that are respectively located between the groove pairs 102', 104'; 104',106', and 106', 108'. The lug 232 servers as a fin at one side of thegroove 94', the lug 234 serves as a fin for one side of the groove 108'and the lug 236 serves as fins for the grooves 100' and 102'. When acable is mounted in a groove, its bolt is tightened and the insulationof the cable is compressed against the groove and the fins on eitherside to form a dirt and insect seal.

Dirt and insects are prevented from entering the space between the ledge73 and the extension 75 when cables are not in the grooves 94'-108' inthe following manner. Although only the outer end of the groove 94' isdescribed, it is to be understood that the outer ends of all the othergrooves 96'-108' will be constructed in the same way. The outer end ofthe groove 94' is enlarged so as to form a semicircular ledge 276, and amatching semi-circular notch 278 is formed in the wall 222 of theprojection 75 from the cover 64 so as to form a circular opening 276,278 when the cover 64 is closed. When no cable is present in the groove94', a cylindrical shank 280 of a resilient plug 282 is thrust throughthe opening, 276, 278, and along the groove 94' to the wall 206, therebyblocking the pair of openings 204' through which the leads of a cableare to be thrust. The diameter of the shank 280 is the same as thediameter of the groove 94'. When in this position, an enlarged head 284of the plug 282 is diametrically compressed in the opening 276, 278 soas to prevent dirt and insects from entering the space between the ledge73 and the extension 75.

When a plug like 282 is removed and a cable is inserted, further dirtand insect sealing is provided in the following manner. The cover 64 isopened, the plug 282 is removed, and a cable is placed into a groovelike 94' with its insulated leads inserted in the openings 204', andwhen the cover 64 is closed, the semi-circular ledge 276 and thesemi-circular notch 278 fit snugly around the cable so as to block dirtand insects from entering into the space between the ledge 73 and theextension 75.

FIG. 13 is the top view of the preferred junction box assembly of FIG.12 with the cover 64 open. It is the same as FIG. 4 except for the meansfor clamping the power cables in position involving the use of the plate238. The plate 242 is not shown so that the fins 270, 272, and 274 maybe seen.

FIG. 14 is the top view of the preferred junction box assembly of FIG.12 with the cover 64 removed and is the same as FIG. 6 except for themeans for clamping the power cables into position involving the plates238 and 242.

FIG. 15A is a section 15A, 15A of FIG. 14 showing the IDC 82 in its openposition. The details are the same as described in connection with FIGS.8C and 8D. The clamp bolt 250 is shown in its raised position thatpermits the power cable 148 to pass under it. FIG. 15B is a section 15B,15B of FIG. 14 showing the IDC 80 in a closed position just before theinsulation of the lead 154 is cut. The power cable 158 is now clamped inposition by the clamp bolt 250. In FIGS. 15A and 15B, the circuit board76 is preferably slightly tilted as indicated.

FIG. 16 is a front view of the junction box assembly of FIG. 12 with itscover 64 removed so that the alignment of the semi-circular ledges like276 with the semi-circular grooves 94'-100' and the openings 204'through which leads are thrust into the IDC's can be better seen. As inFIGS. 9A and 9B a partial section of the sealing chamber 116 is shown inwhich the positions of the openings 190 are shown in dashed lines.

FIG. 17 is a larger view of the plug 282 of FIG. 12, and FIG. 18 showsthe front view of the junction box assembly of FIG. 12 with the cover 64closed and plugs like plug 282 of FIG. 17 inserted through openings like276, 278, and along the semi-circular groves 94'-100' that are not seenbecause of the heads 284 of the plugs. No plugs are inserted along thesemi-circular grooves 102'-108' so that the openings defined by asemi-circular groove such as 276 and a notch such as 278 are clearlyseen.

FIG. 19 is a view like that of FIG. 16 but differs therefrom in thatbolts 246', 248', 250', and 252' differ from the bolts 246, 248, 250,and 252 of FIG. 16 by having curved heads 262', that are swivelled so asto obtain a tighter grip on a power cable. This is the preferred form ofbolt that may be used in FIG. 12, for example.

In FIG. 14, the ends of two passageways or through holes 300 and 300'(also see FIG. 13) are visible through notches in the circuit board 76.FIG. 20 is a cross-section 20, 20 through one of them, but a similarcross-section of the other would be the same. As can be seen in FIG. 20,the passageway 300 extends from the compartment 56 to the compartment 26and contains a filter 302 in accordance with an aspect of thisinvention. The purpose of the filter 302 is to prevent high frequenciespresent in the compartment 26 from entering the compartment 56 while atthe same time permitting the low frequency that is used for power topass from the compartment 26 to the compartment 56.

A terminal 304a of the filter 302 is in the compartment 56, and althoughnot shown, is connected to an appropriate point in the circuit board 76.As previously explained, the circuit of the circuit board 76 connectslow frequency voltage from the filter 302 to the IDC's in thecompartment 56. Adjacent the terminal 304a is a capacitor C1. A terminal304b at the other end of the filter 302 extends into the compartment 26.Adjacent the terminal 304b is a capacitor C2.

The capacitors C1 and C2 are preferably of the ceramic feed throughtype. As shown in FIG. 22, the capacitor C1 is comprised of a ceramiccylinder 306a having a metal annulus 308a mounted around its center. Thecorresponding parts of the capacitor C2 are designated by the samenumber with a subscript b.

As shown in the schematic circuit of the filter 302 shown in FIG. 23,one side of each of the capacitor C1 and C2 is connected to ground andan inductor L1 is connected between their other sides to form a π filterthat passes low frequencies and attenuates high frequencies.

As shown in FIG. 22, the inductor L1 is formed by winding an insulatedwire 310 around a body 312 having the terminals 304a and 304b embeddedin opposite ends thereof. Although not shown, one end of the wire 310 isconnected to the terminal 304a, and the other end is connected to theterminal 304b.

The structure just described is mounted within a metal cylinder 313having external threads 314 adjacent a nut shaped portion 316 at oneend. An annular shelf 318 is formed within the outer end of the nut 316,and an annular shelf 320 is formed within the other end of the cylinder313. Note that the cross-section of the body 312 is reduced where theinsulated wire 310 is located so as to form a space between the wire 310and the cylinder 313 for the purpose of providing better insulationbetween them.

When the components of FIG. 22 are assembled as shown in FIG. 21, theterminals 304a and 304b are respectively inserted the longitudinalopenings 322a and 322b within the ceramic cylinders 306a and 306b. Theannulus 308a is nested in the annular shelf 320 and soldered thereto,and the annulus 308b is nested in the annular shelf 318 and solderedthereto. The terminal 304a is soldered to the opening 322a, and theterminal 304b is soldered to the opening 322b.

As shown in FIG. 20, the filter 302 is mounted within the passageway 300by screwing the threads 314 into mating threads, not shown, in one endof the passageway 300 with the aid of the nut 316. A connection, notshown, is made between the terminal 304a and an appropriate point in thecircuit on the circuit board 76, and a connection, 324 is made betweenthe terminal 304b and an appropriate point in a circuit on a circuitboard 326. The circuit board 326 couples the coaxial port 24 at one endof the compartment 26 to the coax connector 46 (see FIG. 3) at the otherend. Note passageways 300 and 300' are preferably circular.

In accordance with an aspect of this invention, it is important that thecapacitors C1 and C2 be respectively connected to the metal of thecompartments 56 and 26, i.e. at the ends of the metal passageway 300.Stating this in another way, the filter 302 must be mounted between thecompartments 26 and 56. RF energy in the compartment 26 would be pickedup directly by the wire 304b, but it is immediately shorted to ground byC2, and since the inductor winding 310 is completely enclosed in thecylinder 313, no r.f. energy can be picked up by the winding. The r.fenergy is attenuated by the filter between its input 304b and its output304a. Similarly, any r.f. radiation signal picked up or existing in thecompartment 56 will not be conveyed to the compartment 26. Thisstructure overcomes the problem encountered in the prior art wherein theunshielded inductor of the filter is exposed to at least one compartmentthereby creating a situation where r.f. energy picked up by the inductorin one compartment is passed into the other compartment. The presentinvention insures that the filter blocks such high-frequency r.f. energyflow, passing only low-frequency power.

It will be apparent to those skilled in the art that a low pass filterhaving a schematic circuit of a different configuration from that shownin FIG. 23 could be use, but it has to have an input in the innersurface of one compartment and an output in the inner surface of othercompartment so that high frequency signals from one compartment areattenuated by the entire filter before reaching the other compartment.

Although various embodiments of the present invention have been shownand described herein, they are not meant to be limiting. Those of skillin the art may recognize certain modifications to these embodiments,which modifications are meant to be covered by spirit and scope of theappended claims.

What is claimed is:
 1. Apparatus for clamping electric cables to ajunction box having a compartment with a removable cover so as toprevent dirt and insects from reaching a row of pairs of holes in a sideof the compartment through which leads from the cables are to be passedcomprising:a ledge extending from said side of said compartment parallelto and spaced from one side of said row of holes, said ledge having aperiphery; grooves in said ledge respectively, in registration with saidpairs of holes; a projection from said cover having a wall and two endsthat are in contact with the periphery of said ledge when said cover isclosed; notches in the wall of said projection in registration with saidgrooves; fins on both sides of each of said grooves having tops that areat a given distance from said ledge; a plate mounted in contact with thetops of said fins; and threaded bolts mounted in said platerespectively, in registration with said grooves whereby said cables insaid grooves can be secured by advancing the bolts in registration withrespective said grooves in which they are located.
 2. Apparatus as setforth in claim 1 further comprising:a semi circular ledge in an end ofeach of said grooves that is remote from said side of said compartment;and each of said notches in the wall being semi circular so as to matchthe semi circular ledges in the ends of the grooves and thereby form acircular opening when said cover is closed.
 3. Apparatus as set forth inclaim 2 further comprising:at least one resilient plug having a shankwith the same diameter and length as said grooves and a head that isslightly greater in diameter than said circular openings; whereby an endof said shank is in contact with said side of said compartment so as toclose off a respective one of said pairs of holes when said shank is ina respective one of said grooves and said head of said plug isdiametrically compressed between said semi ledge and said semi circularnotch when said plug is positioned in said respective one of saidgrooves with the cover open and the cover then closed.